Telecommunication systems in general and local call systems more specifically, employing radio-broadcast message signals are presently largely employed to ensure the calling of pagers with the purpose of sending information selectively to them from a central station. Such information is transmitted by means of coding schemes and predetermined message formats such as those known under the acronyms POCSAG or GOLAY.
One of the major problems which is encountered in the development and commercialization of pagers concerns the energy supply thereto and more specifically its operational autonomy when the pager is portable, taking into consideration the energy storage capacity of the energy source incorporated into the pager.
For example, pagers presently exist on the market produced in the form of a timepiece which in addition to assuring the pager function is also given the possibilities of indicating the time of day and other timekeeping functions such as the indication of elapsed time, the date and the day of the week. In such arrangements, which are preferably worn as a wristwatch, the dimension of the energy source is naturally of very great importance. The smaller such dimension is, the more one can reduce the dimensions of the timepiece and, proceeding therefrom, obtain more facilities for conceiving a timepiece having an agreeable design, such condition being essential in order to render the timepiece saleable in mass quantities.
Up to the present, the manufacturers of known pagers have only very partially attained this objective of very small consumption. Consequently, they are accustomed to providing pagers with a rather voluminous energy source in order to attain a compromise between an acceptable autonomy and a size compatible with easy handling and daily transport by the user on his person. If a good compromise of this type is relatively easily attainable for a pager carried in a pocket of the clothing, for instance, it is by no means the same when it is necessary to house at the same time a pager, a timepiece and an energy source in a volume as small as that of a watch worn on the wrist. Pagers of this nature already on the market have certainly the required volume, even though their design often leaves something to be desired, but on the other hand they have a relatively feeble autonomy. Thus, there exist pager watches in which, in order to be able to house a battery of sufficient size, there is provided on the case a housing which lateraly overflows the perimeter covered by the dial or, more generally, the display arrangement. Such protuberance evidently spoils the design of the assembly in a manner that in such an embodiment, a good compromise between autonomy and volume (or design) is not attained.
Specialists in the domain of pagers know that the greatest consumer of energy in the pager is the receiver which, from the antenna, is charged with receiving the modulated carrier transmitted by the central station and demodulating such carrier in order to extract therefrom the useful binary signal. Various propositions have thus been made in the past in order to avoid operation of the receiver during the entire time that the user maintains the pager turned on or under energization.
Certain of these propositions foresee simply providing the pager with a time circuit capable of cutting the energization of the pager in an arbitrary manner, for example during the night when the user, having then no need of the pager, has forgotten to turn it off. This solution is not by itself satisfactory in order to attain a very small consumption.
Other more sophisticated solutions consist in rendering the cut-off periods of the pager a function of the form or type of received signal. Such a solution is described for instance in the patent U.S. Pat. No. 4,370,753 in the framework of radio-broadcast message signals including a preamble followed by a certain number of messages representing the information to be transmitted. In this case, a control circuit periodically connects the energy source to the receiver in order that a frequency detector may recognize in the received signal preamble a sequential code belonging to the pager under consideration and this according to a special form bringing on multiple recognition. Once the code has been recognized, the receiver is placed under tension during an extended period capable of covering the duration of several consecutive messages contained in the received signal. This solution effectively permits placing the receiver into operation only during reduced periods and one thus succeeds in economizing the energy consumed by the pager. However, the receiver remains supplied during long periods and does not take into account the fact that the radio-broadcast signal contains a great quantity of information which is not useful for one pager under consideration, but in fact is addressed to other pagers forming part of those to which the radio-broadcast signal is sent. Furthermore, under certain operating conditions, a pager has generally no need to process the entire contents of the information which reaches it, even if such is more specifically destined for it, for example in order to permit it to be synchronized with the rhythm of the transmitter of the radio-broadcast signal.
Another solution is described in patent EP 0 118 153. In this case it concerns a pager specifically intended to work with the POCSAG format. The circuit of this pager also permits cutting off the energization of the receiver under certain operating conditions as is permitted by the POGSAG format. More precisely, in supposing that the pager has already assured its synchronization with the bits of the received message signal and also with the groups of synchronization and message code words (addresses and message information) an energization control circuit authorizes energization of the receiver during the period of each synchronization code word and each signal frame which is allocated to such pager within a group of message code words. This circuit thus enables obtaining a better energy economy than the pager of the previously cited US patent.
However, the recognition of synchronization or address code words can only take place after reception of the totality of these words, for which procedure all the bits of such words must necessarily be checked in their totality and subjected to an error analysis. It results therefrom that such a pager still presents a relatively high energy consumption taking into account the fact that a group of code words in the POCSAG format is presented each second during the broadcast of a data packet by the central transmitter, this operation itself being repeated every one to two minutes.
The invention is based on the determination that the energization periods of a pager receiver can be still further reduced without spoiling either good synchronization or good analysis of the message information intended for the pager under consideration.
The purpose of the invention is to create a pager in which the receiver is energized only during the time which is strictly necessary in order to permit correct interpretation of the information intended therefor, that is to say, without changing the success call rate, such pager thus permitting obtention of a good compromise between its autonomy and its general dimensions.
The invention also has as purpose to create a pager which may be advantageously, although not exclusively, provided in the form of a wristwatch capable, in addition to offering the pager functions, to provide one or several horological functions such as indication of the time of day and the date for example.